I've been interested in a lift for my Xterra and was wondering what the difference was between a suspension lift and a body lift? Also which one is better?

Well what do you want.

Perfomance as in more travel?
More clearance to fit bigger tires?
A taller look?
How much do you want to spend?

Body lifts are cheap but do not offer any more performance in suspension. They do allow you to fit larger tires.

Give me a bit more info.

I'd suggest reviewing topics in the suspension section. That's were all lifts, suspension and body, are typically discussed even though body lifts have nothing to do with the suspension.